One known example of an incandescent lamp which the present invention is designed to replace, includes a base, a bulb, and a pair of tungsten filaments of the cross axis, coil type.
There have been difficulties in the past in providing a tungsten-halogen lamp capable of providing sufficient luminance when utilizing a low wattage coil configuration (such as one of less than fifteen watts). It has been observed that the coil temperature, which is primarily instrumental in governing luminance, falls off rapidly from the central portion to the opposed end portions of the filament. This temperature variation is due to the adjacent coils heating each other in the central portion, while the two opposed end portions are heated primarily on the side closest to the central portion, the temperature tapering off as the ends are reached. In low wattage filaments, the number of single coil turns is relatively small and thus the percentage of coil turns that is radiating efficiently in the visible region is relatively low.